The useful service life of a rotary cutting tool such as a thread-cutting tap is very significantly enhanced by supplying pressurized coolant, typically oil, to the cutting edges of the flutes of the tap. In this manner, heat is very efficiently dissipated from the cutting tap and the workpiece, with the flow of coolant desirably flushing away chips of material being cut by the tool. In practice, machining efficiency is significantly improved due to extended tool life, reduced downtime attendant to tool breakage and replacement, and reduced piece part reworking or scrapping.
One manner in which pressurized coolant fluid is supplied to the cutting edges of a tap entails the delivery of pressurized coolant from an associated machine tool spindle through a bore extending axially through the tap. Tap-receiving tool holders having coolant delivery arrangements are employed for this purpose, and are configured to provide a flow passage for the coolant from the spindle to the axial tap bore.
This type of cutting tap and coolant delivery arrangement is particularly suited for effecting tapping in a blind hole, since pressurized coolant flows from the tip of the tap back along the tap shank between its flutes, thus cooling the tap and flushing away chips as the coolant flows from the blind hole. However, it will be appreciated that this type of tap cooling arrangement is not suited for through hole tapping, since coolant flowing from the tip of the tap tends to merely flow away from the tap through the hole, rather than back along the shank of the tap.
Accordingly, it is very desirable to provide an arrangement for providing pressurized coolant to a cutting tap which acts to cool the tap and flush away chips during through hole tapping. Most preferably, such an arrangement should lend itself for use with taps having an axial coolant bore for blind hole tapping, as well as with solid taps employed during through hole tapping.